So i have this problem that whenever i get to around 50 MPH or so my car starts slightly vibrating. sometimes it does it worse than others and sometimes it doesnt seem to do it at all. I have 18" rims on it with an aftermarket suspension. Does anyone know what this could be please let me know. The car only has roughly 31,000 miles on it so its still quite new. Thanks

Low tire pressure, Tire weight missing in which causes tire to be unbalanced.

ok ill check that today and see if it helps. thanks

Are you using hub-centric rings on your 18" rims? I'd start there and/or get them balanced.

that happened to me. My problem was that it was a bent rim.

where would i get hub-centric rings at?

At the place you bought your rims.